Skin packaging is essentially a vacuum forming process; and, in a typical prior art process, a sheet of thermoplastic film is placed in a frame, and below the frame is a vacuum plate upon which a piece of backing board or a supporting member is placed. The product to be skin packaged is positioned on top of the backing board and heat is applied to the thermoplastic film in the frame. When the film has been heated to become sufficiently soft, the frame is lowered and the plastic sheet drapes itself over the product. As this happens, a partial vacuum is created through the vacuum plate and the air underneath the plastic film is withdrawn through the backing board. The air pressure differential between the top and bottom of the plastic sheet causes the sheet to be tightly pressed around the product. The film may be coated with an adhesive or the backing board may be so coated. Where the two contact each other, a strong bond is formed resulting in a package in which the product is tightly held to the backing board for safe shipping and for subsequent rack display in retail stores.
Vacuum skin packaging differs from the above described skin packaging process in that both thermoplastic film and the backing board are impervious to gases and the resulting package can be evacuated and hermetically sealed, if desired. The same end result is sought, i.e. the product is to be tightly held by transparent film to the backing board. The conventional method employs a backing board which is porous or which is perforated so that the vacuum may be drawn directly through the backing board. The vacuum skin packaging process generally employs a vacuum chamber with an open top. The product on a impervious backing board is placed on a platform within the vacuum chamber. The top of the chamber is then covered by a sheet of film which is clamped tightly against the chamber to form a vacuum type closure. The chamber is evacuated while the film is heated to forming and softening temperatures. The platform can then be raised to drive the product into the softened film and air pressure can be used above the film to force it tightly around the product. This type of process is disclosed in French Pat. No. 1,258,357 issued to Alain G. Bresson on Mar. 6, 1961. A refinement to the process described in the Bresson French patent is disclosed in French Pat. No. 1,286,018 which issued on Jan. 22, 1962 to Laroach Freres, Ltd. In the Laroach Freres process, after the chamber has been evacuated and the product driven into the heat softened film, the vacuum is released and ambient air is permitted to enter the chamber so that the thermoplastic film molds more or less on the product since there is a vacuum on the product side of the film and ambient air pressure on the other side of the film.
In Australian Pat. No. 245,774 which issued to Colbro Proprietary Ltd. and Cole and Son Proprietary Ltd. on July 16, 1963, a vacuum skin packaging process is described in which an article to be packaged is inserted within the lower half of a vacuum chamber on a backing board, a thermoplastic film is placed over the open face of the lower half of the chamber, the chamber is closed and both halves are brought to essentially the same state of vacuum, the film heated and softened, and then atmospheric air is introduced into the upper half of the chamber so that it alone forces the thermoplastic film down around the product and against the backing board.
Still another variation of the vacuum skin packaging process which can be found in the prior art is that disclosed in U.S. Pat. No. 3,491,504 which issued to W. E. Young et al on Jan. 27, 1970. The Young patent discloses a process in which the softened film can be physically moved down over a stationary product and, in combination with air pressure, the softened thermoplastic film will be molded onto the product.
In U.S. Pat. No. 3,694,991 which issued on Oct. 3, 1972 to Richard R. Perdue et al, a vacuum skin packaging process is disclosed in which the product to be packaged is placed on a gas impervious supporting member, a flexible sheet is shaped into a concavity, and this sheet is positioned over the product covering same but not contacting either the product or the supporting member. Next, gases are evacuated from the space between the sheet and supporting member and then the sheet is moved from its concave position so that it closely contacts the product and supporting member so that the sheet may be sealed against the supporting member. Also, in U.S. Pat. No. 3,736,721 issued on June 5, 1973 to Robert O. Wolfelsderger, a vacuum skin packaging process is disclosed in which the backing board or support member is eliminated and the product is entirely sealed within two film portions which meet in a peripheral sealed in the midplane of the product. Thus, film sheet is vacuum formed to conform to the shape of both the upper half and the lower half of the product.
In each of the foregoing described prior art vacuum skin packaging processes, a skin package is formed on only one side of a support member of film member. It is one object of the present invention to provide a skin package in which products are skin packaged to both sides of a single film or supporting member.
It is another object of the present invention to provide a vacuum skin package in which one portion of the package may be opened without destroying the hermetic seal enclosing the products in the remainder of the package.
It is yet another object of the present invention to provide a skin package which makes use of a single, central support member thereby effecting a saving in materials and energy to produce the package.
It is yet another object of the present invention to provide a novel skin package which was not heretofore available in the art.
All of the foregoing listed advantages and others will be readily apparent to those conversant in the art of skin packaging from the following summary of the invention and detailed description.